It's pretty good and easy to use. Definitely the best free x86 hosted virtual machine software.

You just need an installer ISO of the OS you want. Decide how much storage and RAM you need beforehand, go through the typical OS installation steps, and just use the same way as a host computer. You don't need to even mess with drivers or anything complicated like that with any remotely modern Windows/Linux guest.

It's not particularly great at video acceleration or a lot of other advanced features though. Don't bother playing 3D games in it unless you know how to deal with PCIe passthrough.

You'll want to run it on a computer with plenty of free disk space and plenty of RAM if you want decent results.